The focus of this project is the analysis of multistage neoplastic change in B-cell lymphomas induced in the bursa of Fabricius by myc oncogenes. A central experimental strategy involves retroviral gene transfer into bursal stem cells used to reconstitute ablated embryonic bursal follicles. This approach, together with related techniques, allows further insight into the roles in bursal lymphomagenesis of apoptiotic cell death, cell cycle control, genetic instability, and the genes which regulate these processes-including a novel gene we have detected, CTCF, which can regulate myc expression. Our specific aims are: (1) We will analyze the biological function of CTCF by determining the phenotypic consequences of CTCF overexpression and inhibition in normal fibroblasts, cultured B-cell lines, cultured bone marrow and in normal and neoplastic B-cell development in vivo. (2) We will block apoptotic cell death in normal and preneoplastic bursal follicles by constitutive overexpression of NR-13 and/or other cell death regulatory genes. In this fashion, we will learn more about the role of all death in both normal and neoplastic bursal development. (3) We will analyze the relationship between surface immunoglobulin (Ig) diversification, apoptotic cell death and cellular proliferation, in normal and neoplastic bursal B-cells. These studies involve observation of the effects of constitutive expression of germline Ig surface molecules in bursal stem cells and their normal, preneoplastic and neoplastic progeny. (4) We will determine whether bic can act as a cooperating oncogene in the generation of myc-initiated B-cell lymphoma and will explore the mechanisms underlying activation of bic expression in these tumors.